Polymer Solar Cells: Effects of Annealing Treatment and Polymer Blends on I-V Characteristics

Abstract

This research reports on a fabrication of polymer solar cells based on blends of two widely used polymeric semiconductors with [poly(2-methoxy-5-(3,7-dimethyloctyloxy)-para phenylene vinylene)] (MDMO-PPV) and the soluble fullerene C60 derivative [6,6 phenyl C61-butyric acid methyl ester] (PCBM). These polymers act as an active layer for bulk heterojunction photovoltaic devices. The device was fabricated on an indium tin oxide (ITO) coated glass substrate with a sheet resistance 8-12 Ω/square. After cleaned and dried the substrate, a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in H2O was spin coated onto the freshly prepared substrate using an adhesive tape mask. The mask was then removed, and the substrate was dried in a vacuum oven at 120ºC for 60 minutes. The device and then masked again and a blend of MDMO-PPV and PCBM in chorobenzene was then spun coated on top. The mask was removed and transferred to an evaporator where an aluminum was coated through a shadow mask to define an active device area of 2,6 cm2. Some of the devices then annealing in a vacuum oven at 60ºC for 60 minutes. The sealant was placed between the back of the device and a glass slide, and then cured in an oven with a temperature of 100 ºC for 10 minutes in vacuum condition. For characterization, the device was illuminated with a mercury lamp at the intensity of 27 mW/cm2 and the temperature approximately 25ºC. The influence of the annealing treatment and polymer blends on the photovoltaic performance of the device is observed here. The best performance was obtained from the device with a blend ratio of 1:1 MDMO-PPV/PCBM without annealing treatment. The typical power efficiency was 0.001 % with open circuit voltage of 0.347 V, short circuit current of 0.064 mA, and maximum power of 0.006 mW.